Vector diffraction analysis of optical disk readout

The optical disk readout signals from ROM disks are presented by use of a rigorous three-dimensional vector diffraction method. The optical disk is modeled as a crossed metal grating without restriction on the form of the information marks, and the permittivity of the metal is taken into account. The diffracted field from the disk is obtained by means of decomposing the focused incident beam into a spectrum of plane waves and then calculating the diffracted plane waves for each respective incident component. The readout signal is obtained by integration of the energy-flux density of the diffracted field according to the detection scheme of the optical disk system. A typical digital versatile disk (DVD) system is applied with this theory, and the result is far from that of scalar diffraction theory.     

Optical readout for optical storage with phase jump

A novel, to our knowledge, optical readout for optical storage with phase jump is presented. In the readout scheme two coherent laser beams are focused on an optical disk with one beam scanning along pits and the other along land. When the probe beam scans across a pit, two phase jumps will take place in the interference resultant of the two beams if the phase difference between two beams is prefixed at pi, resulting in a phase pulse of 180 deg. The slopes of rising and falling edges of the phase pulse are infinite, and they are not affected by the intensity variation of the light source, stray light, and the vibration of the disk. Therefore this phase pulse can be used to read out the information on an optical disk. The use of phase jump will improve the signal-to-noise ratio of the readout signal and enhance the density of optical storage. An optical readout with phase jump was constructed. Both the theoretical design and the experimental verification are conducted. Experimental results show that the proposed optical readout is feasible.     

Angular motion point spread function model considering aberrations and defocus effects

When motion blur is considered, the optics point spread function (PSF) is conventionally assumed to be fixed, and therefore cascading of the motion optical transfer function (OTF) with the optics OTF is allowed. However, in angular motion conditions, the image is distorted by space-variant effects of wavefront aberrations, defocus, and motion blur. The proposed model considers these effects and formulates a combined space-variant PSF obtained from the angle-dependent optics PSF and the motion PSF that acts as a weighting function. Results of comparison of the new angular-motion-dependent PSF and the traditional PSF show significant differences. To simplify the proposed model, an efficient approximation is suggested and evaluated.     

Rewritable optical-disk fabrication with an optical recording material made of naphthalocyanine and polythiophene

A novel rewritable optical disk that uses an optical recording material made of naphthalocyanine and polythiophene as the recording layer is described. In this system the complex refractive index of the recording material changes reversibly, depending on the aggregation states of naphthalocyanine induced by a conformation change of the polythiophene matrix. After recording, the imaginary part of the refractive index of the recording material increases to three times that of the unrecorded part, at a wavelength of 790 nm at which a semiconductor laser emits light. The fabricated polythiophene naphthalocyanine optical disk shows a high reflectivity of 58% and a large readout modulation amplitude (I(11)/I(top)) of 0.63. It is confirmed that the polythiophene/naphthalocyanine optical disk can be played back on conventional compact-disc players even after ten cycles of rewriting.     

Theoretical analysis of a thermally induced superresolution optical disk with different readout optics

Simulations have been performed to evaluate the effect of a thermal-induced mask on the performance of an optical disk. For simplicity and also so as not to lose generality, we first assume that the thermal-induced mask can be represented by an ellipse with variable shape and a relative position with respect to the center of the readout laser spot. Simulation results reveal that the optical disk exhibits a maximum response when almost half the laser spot is covered by the mask. With a conventional single-beam readout technique, however, this can hardly be achieved. The possibility of achieving this by use of an assistant beam with a modified beam profile is discussed. We show that this method allows us to obtain a maximum response in the track direction without any degradation in the radial direction.     

Behavior of the point-spread function in photon-limited confocal microscopy

We study the behavior of the point-spread function (PSF) of the confocal scanning optical microscope (CSOM) when the available optical energy density from the sample plane is low (<7.5 microJoule/micrometers2). The PSF profile is analyzed under three photon-limited imaging conditions: (1) reflection-type CSOM with a weak source and a perfectly reflecting sample, (2) reflection-type CSOM with a strong illumination source and a weak sample, and (3) fluorescence CSOM with a weak fluorescent sample. Linfoot's image quality criteria of fidelity, structural content, and correlation quality are used to assess the reproducibility of the PSF profile as a function of the photon number. Low photon numbers yield a PSF profile that is difficult to maintain from one location in the sample plane to another. The optical sectioning capability of the CSOM was found to deteriorate more quickly against light power reduction than its transverse resolving power. The signal-to-noise ratio of the scanned CSOM image improves exponentially with the photon number from the sample plane. The noise that is generated by an unstable PSF has an average amplitude that decreases exponentially with the photon number and is significant only at low photon numbers. The CSOM image quality deteriorates because of spurious high-frequency components, degradation in the PSF dynamic range, and varying resolving power.     

An Infrared Diagnosis Channel for an Electronuclear Installation

A data-acquisition system is described for use with fast thermal processes in an electronuclear installation. The diagnostic channel consists of an optical system, coordinate-sensitive detector, and electronic units for amplifying, processing, and managing the data and interfacing with the computer. The data readout works under the real-time disk operating system.     

Digitized molecular diagnostics: reading disk-based bioassays with standard computer drives

We report herein a digital signal readout protocol for screening disk-based bioassays with standard optical drives of ordinary desktop/notebook computers. Three different types of biochemical recognition reactions (biotin-streptavidin binding, DNA hybridization, and protein-protein interaction) were performed directly on a compact disk in a line array format with the help of microfluidic channel plates. Being well-correlated with the optical darkness of the binding sites (after signal enhancement by gold nanoparticle-promoted autometallography), the reading error levels of prerecorded audio files can serve as a quantitative measure of biochemical interaction. This novel readout protocol is about 1 order of magnitude more sensitive than fluorescence labeling/scanning and has the capability of examining multiplex microassays on the same disk. Because no modification to either hardware or software is needed, it promises a platform technology for rapid, low-cost, and high-throughput point-of-care biomedical diagnostics.     

Effects of point-spread function on calibration and radiometric accuracy of CCD camera

The point-spread function (PSF) of a camera can seriously affect the accuracy of radiometric calibration and measurement. We found that the PSF can produce a 3.7% difference between the apparent measured radiance of two plaques of different sizes with the same illumination. This difference can be removed by deconvolution with the measured PSF. To determine the PSF, many images of a collimated beam from a He-Ne laser are averaged. Since our optical system is focused at infinity, it should focus this source to a single pixel. Although the measured PSF is very sharp, dropping 4 and 6 orders of magnitude and 8 and 100 pixels away from the point source, respectively, we show that the effect of the PSF as far as 100 pixels away cannot be ignored without introducing an appreciable error to the calibration. We believe that the PSF should be taken into account in all optical systems to obtain accurate radiometric measurements.     

Partial-response signaling for phase-change optical data storage without electronic equalization

We describe the application of partial-response (PR) signaling in rewritable phase-change optical data storage. No electronic filter is necessary to shape the readout signal to a certain PR target. A PR-like waveform at the output of the read channel is directly achieved by optical recording. A genetic algorithm is used to optimize the parameters for writing and therefore to minimize the difference between the actual readout signal and the ideal PR waveform. With a laser wavelength of 0.66 microm and an objective lens with a numerical aperture of 0.6, four linear densities were examined: 0.4, 0.3, 0.25, and 0.2 microm/bit (without modulation). Results showed that the linear density of 0.25 microm/bit can be realized on a rewritable digital-versatile disk.     

Readout characteristics of a near-field optical probe as a data-storage readout device: submicrometer scan height and resolution

A photodiode-embedded near-field scanning microscope cantilever (photocantilever) was used to scan in a noncontact, constant-height mode at a range common in hard disk drives to examine its readout capabilities when mounted on a flying-slider head. The intensity ratios of spatial frequencies that compose the obtained near-field image were analyzed by use of the fast Fourier transform. A simplified model was developed as a guiding principle for estimating the readout characteristics of the near-field optical probe in the above-proximity scan-height range.     

Three-dimensional remote sensing by optical scanning holography

A technique is presented by which holograms can be recorded when an object or scene is scanned with an optically heterodyned Fresnel zone pattern. The experimental setup, based on optical scanning holography, is described and experimental results are presented. We apply the scanning holography technique to three-dimensional reflective objects for the first time to our knowledge and address the unique requirements for such a system. We discuss holographic recording and numerical image reconstruction using a system point-spread function (PSF) approach. We demonstrate numerical image reconstruction of experimentally recorded holograms by two techniques: deconvolution with a simulated PSF and an experimentally acquired PSF.     

Scale-tunable optical correlation with natural light

We describe two different scale-tunable optical correlators working under totally incoherent light. They behave as spatially incoherent wavelength-independent imaging systems with an achromatic point-spread function (PSF). In both cases it is possible to adapt the scale of the achromatic PSF, i.e., to modify the scaling factor of the PSF and preserve the chromatic compensation, by one's shifting the input along the optical axis. The remarkable properties of these systems allow us to carry out a scale-tunable color pattern-recognition experiment with natural light.     

Gradient-index human lens as a quadratic phase transformer

The correspondence between the linear integral transform and the ray-transfer matrix of a first-order optical system is used to evaluate the transmittance function of gradient-index (GRIN) human lens regarded as a quadratic phase transformer. The size of the GRIN crystalline lens has been considered for redefining the effective transmittance function by the pupil function. The role that the GRIN nature of the human lens plays in the retinal image quality using the point spread function (PSF) is commented on. The simulation results show that the effective radius of the output face of the lens decreases with increasing thickness and that it is higher for flat end surfaces than for curved end faces. On the other hand, the simulation results also show, for small pupil sizes, that the GRIN nature of the human lens is a retinal image degradation source producing the spread of the PSF and that the curved end surfaces of the lens constitute a retinal image quality improve factor contributing to the narrowing of the PSF.     

Parametric blind deconvolution: a robust method for the simultaneous estimation of image and blur.

Blind-deconvolution microscopy, the simultaneous estimation of the specimen function and the point-spread function (PSF) of the microscope, is an underdetermined problem with nonunique solutions that are usually avoided by enforcing constraints on the specimen function and the PSF. We derived a maximum-likelihood-based method for blind deconvolution in which we assume a mathematical model for the PSF that depends on a small number of parameters (e.g., less than 20). The algorithm then estimates the unknown parameters together with the specimen function. The mathematical model ensures that all the constraints of the PSF are satisfied, and the maximum-likelihood approach ensures that the specimen is nonnegative. The method successfully estimates the PSF and removes out-of-focus blur. The PSF estimation is robust to aberrations in the PSF and to noise in the image.     

Optimal apodization design for medical ultrasound using constrained least squares part I: theory

Aperture weighting functions are critical design parameters in the development of ultrasound systems because beam characteristics affect the contrast and point resolution of the final output image. In previous work by our group, we developed a metric that quantifies a broadband imaging system's contrast resolution performance. We now use this metric to formulate a novel general ultrasound beamformer design method. In our algorithm, we use constrained least squares (CLS) techniques and a linear algebra formulation to describe the system point spread function (PSF) as a function of the aperture weightings. In one approach, we minimize the energy of the PSF outside a certain boundary and impose a linear constraint on the aperture weights. In a second approach, we minimize the energy of the PSF outside a certain boundary while imposing a quadratic constraint on the energy of the PSF inside the boundary. We present detailed analysis for an arbitrary ultrasound imaging system and discuss several possible applications of the CLS techniques, such as designing aperture weightings to maximize contrast resolution and improve the system depth of field.     

Analog signal acquisition from computer optical disk drives for quantitative chemical sensing

Optoelectronic consumer products that are widely employed in the office and home attract attention for optical sensor applications due to (1) their cost advantage over analytical instruments produced only in small quantities, (2) robustness in operation due to the detailed manufacturability improvements, and (3) ease of operation. We demonstrate here a new approach for quantitative chemical/biochemical sensing when analog signals are acquired from conventional optical disk drives, and these signals are used for quantitative detection of optical changes of sensor films deposited on conventional CD and DVD optical disks. Because we do not alter manufacturing process of optical disks, any disk can be employed for deposition and readout of sensor films. The optical disk drives also perform their original function of reading and writing digital content to optical media because no optical modifications are introduced to obtain the analog signal. Such a sensor platform is quite universal and can be applied for chemical and biological quantitative detection, as well as for monitoring of changes of physical properties of regions deposited onto a CD or DVD (e.g., during combinatorial screening of materials). As a model example, we demonstrate the concept using chemical detection of ionic species such as Ca2+ in liquids (e.g., blood, urine, or water). Colorimetric calcium-sensitive sensor films were deposited onto a DVD, exposed to water with different concentrations of Ca2+, and quantified in the optical disk drive. The developed lab-on-DVD system demonstrated a 5 ppm detection limit of Ca2+ determinations, similar or slightly better than that achieved using a conventional fiber-optic portable spectrometer. This detection limit corresponded to a 0.023 absorbance unit resolution, as determined by the measurement of the same colorimetric films with a portable spectrometer. Determinations of Ca2+ unknowns using the lab-on-DVD system demonstrated +/-5 ppm accuracy and 2-5% relative standard deviation precision in predicting 100 ppm Ca2+.     

Readout signals calculated for near-field optical pickups with land and groove recording

Optical disk readout signals with a solid immersion lens (SIL) and the land-groove recording technique are calculated by use of a simplified vector-diffraction theory. In this method the full vector-diffraction theory is applied to calculate the diffracted light from the initial state of the disk, and the light scattered from the recorded marks is regarded as a perturbation. Using this method, we confirmed that the land-groove recording technique is effective as a means of cross-talk reduction even when the numerical aperture is more than 1. However, the top surface of the disk under the SIL must be flat, or the readout signal from marks recorded on a groove decays when the optical depth of the groove is greater than lambda/8.     

Mimicking a hybrid-optomechanical system using an intrinsic quadratic coupling in conventional optomechanical system

We consider an optical and mechanical mode interacting through both linear and quadratic dispersive couplings in a general cavity-optomechanical set-up. The parity and strength of an intrinsic quadratic optomechanical coupling (QOC) provides an opportunity to control the optomechanical (OM) interaction. We quantify this interaction by studying normal-mode splitting (NMS) as a function of the QOC's strength. The proposed scheme exhibits NMS features equivalent to a hybrid-OM system containing either an optical parametric amplifier or a Kerr medium. Such a system in reality could offer an alternative platform for devising state-of-art quantum devices with requiring no extra degrees-of-freedom as in hybrid-OM systems.     

Influence of substrate thickness on optical disk readout

I consider the influence of different substrate thicknesses on the signal obtained from an optical disk. Two solutions are presented for the reading of different disk types. In one situation a substrate thickness change for disks with equal density is made inoffensive by introduction of a combined amplitude-phase mask in the pupil of the readout objective. In a second situation, where the different thickness is accompanied by a change in optical density, a specific selection in the far field of the detected radiation has proven to be adequate.